James Schlesinger, a tenacious, blunt-talking former Pentagon chief who served as a cabinet officer under three US presidents, has died. He was 85.

A Harvard-educated economist who became a powerful figure in the 1970s, as well as an influential nuclear strategist, Schlesinger served as defence secretary under Richard Nixon and Gerald Ford and was named the country's first energy secretary under Jimmy Carter.

Schlesinger was defence secretary between 1973 and 1975, a time of upheaval with US military morale on the decline and the White House preoccupied by the Watergate scandal.

A Republican with hawkish tendencies, Schlesinger clashed with Congress over defence spending and argued for bigger budgets to counter the Soviets. He developed a nuclear strategy that called for retaliatory strikes against Soviet military targets.

During the peak of the Watergate scandal in August 1974, Schlesinger became so concerned about Nixon's emotional state that he ordered the military not to respond to White House orders unless they were cleared by him and secretary of state Henry Kissinger.

He confirmed the instructions years later, which also included plans to deploy troops in the US capital in the event of any turmoil surrounding Nixon's political succession.

Ford retained him as defence secretary but he was dismissed in November 1975, after clashing with Ford and lawmakers.

Before the Pentagon, he served as chairman of the Atomic Energy Commission, which promoted nuclear energy. And in 1973, Nixon named him director of the CIA after the president fired spy chief Richard Helms for refusing to obstruct the Watergate investigation.

In a mere five-month stint at the CIA, Schlesinger learned that intelligence officers who were barred by law from spying on Americans had carried out break-ins in the US on orders from the White House.

He sacked 1,000 of the 17,000-strong work force and ordered a probe into past operations.

After his cabinet positions, he later served on numerous advisory boards, including one for the Pentagon in 2008 looking at problems in the air force's management of nuclear forces.

Agence France-Presse

This article appeared in the South China Morning Post print edition as At the pinnacle of power at a time of US turmoil